1. Field of the Invention
The present invention relates to graphical display apparatus.
2. Description of the Prior Art
It has previously been proposed to employ cathode ray tubes for the display of, for example, alpha-numerical information, particularly for the visual display of data derived from an information store such as is used in electronic data processing apparatus. Such a display is conveniently presented on a cathode ray tube whose electron beam is displaced in a succession of horizontal lines spaced apart in a vertical direction by a raster scan in a manner similar to that employed in the presentation of television pictures. It has also been proposed to display graphical information by causing the electron beam to trace out lines on the tube face. The display of graphical data on a tube driven by a line raster has hitherto presented considerable difficulties in practice due to the considerable amount of data storage required.